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Testing your application

It’s not rare to have to test your application but deploying the infrastructure can be cumbersome. While Docker or Test Containers have improved the testing experience, you may want to mock this infrastructure.

SmallRye Reactive Messaging proposes an in-memory connector for this exact purpose. It allows switching the connector used for a channel with an in-memory connector. This in-memory connector provides a way to send messages to incoming channels, or check the received messages for outgoing channels.

To use the in-memory connector, you need to add the following dependency to your project:

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<dependency>
  <groupId>io.smallrye.reactive</groupId>
  <artifactId>smallrye-reactive-messaging-in-memory</artifactId>
  <version>4.18.1</version>
  <scope>test</scope>
</dependency>

Then, in a test, you can do something like:

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package testing;

import jakarta.enterprise.inject.Any;
import jakarta.inject.Inject;

import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;

import io.smallrye.reactive.messaging.memory.InMemoryConnector;
import io.smallrye.reactive.messaging.memory.InMemorySink;
import io.smallrye.reactive.messaging.memory.InMemorySource;

public class MyTest {

    // 1. Switch the channels to the in-memory connector:
    @BeforeAll
    public static void switchMyChannels() {
        InMemoryConnector.switchIncomingChannelsToInMemory("prices");
        InMemoryConnector.switchOutgoingChannelsToInMemory("processed-prices");
    }

    // 2. Don't forget to reset the channel after the tests:
    @AfterAll
    public static void revertMyChannels() {
        InMemoryConnector.clear();
    }

    // 3. Inject the in-memory connector in your test,
    // or use the bean manager to retrieve the instance
    @Inject
    @Any
    InMemoryConnector connector;

    @Test
    void test() {
        // 4. Retrieves the in-memory source to send message
        InMemorySource<Integer> prices = connector.source("prices");
        // 5. Retrieves the in-memory sink to check what is received
        InMemorySink<Integer> results = connector.sink("processed-prices");

        // 6. Send fake messages:
        prices.send(1);
        prices.send(2);
        prices.send(3);

        // 7. Check you have received the expected messages
        Assertions.assertEquals(3, results.received().size());
    }
}

When switching a channel to the in-memory connector, all the configuration properties are ignored.

Warning

This connector has been designed for testing purpose only. Switching the channel to in-memory connector means that the original connector is not invoked at all during tests. Therefore, if your code depends on a specific connector behaviour or a custom metadata you need to simulate those in your tests.

The switch methods return Map<String, String> instances containing the set properties. While these system properties are already set, you can retrieve them and pass them around, for example if you need to start an external process with these properties:

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public Map<String, String> start() {
    Map<String, String> env = new HashMap<>();
    env.putAll(InMemoryConnector.switchIncomingChannelsToInMemory("prices"));
    env.putAll(InMemoryConnector.switchOutgoingChannelsToInMemory("my-data-stream"));
    return env;
}

public void stop() {
    InMemoryConnector.clear();
}

Note

The in-memory connector support the broadcast and merge attributes. So, if your connector is configured with broadcast: true, the connector broadcasts the messages to all the channel consumers. If your connector is configured with merge:true, the connector receives all the messages sent to the mapped channel even when coming from multiple producers.

Vert.x Context with In-memory Connector

For the sake of simplicity, In-memory connector channels dispatch messages on the caller thread of InMemorySource#send method. However, most of the other connectors handle context propagation dispatching messages on separate duplicated Vert.x contexts.

If this causes a change of behaviour in your tests, you can configure the in-memory connector channels with run-on-vertx-context attribute to dispatch events, including messages and acknowledgements, on a Vert.x context. Alternatively you can switch this behaviour using the InMemorySource#runOnVertxContext method.